Compensated screwdown mechanism for a rolling mill



Nov. 17, 1964 Filed Oct. 30, 195

P. BLAIN COMPENSATED SCREWDOWN MEC HANISM FOR A ROLLING MILL Fig.2

f Fig.1

INVENTOR PHUL BLRIN {MW Nov. 17, 1964 P. BLAIN 3, 57,073

COMPENSATED SCREWDOWN MECHANISM FOR A ROLLING MILL Filed Oct. 50, 1959 5 Sheets-Sheet 2 INVENroR. pF'UL Buy/n HG-E f Nov. 17, 1964 P. BLAIN 3,157,073

COMPENSATED SCREWDOWN MECHANISM FOR A ROLLING MILL Filed Oct. 50, 1959 5 Sheets-Sheet 3 j I 18c I/vvn/ron.

HUL BLRIN P. BLAIN Nov. 17, 1964 COMPENSATED SCREWDOWN MECHANISM FOR A ROLLING MILL Filed Oct. 30, 1959 5 Sheets-Sheet 4 Il/VE/Wbii. nu L 31. H 14/ P. BLAIN Nov. 17, 1964 COMPENSATED SCREWDOWN MECHANISM FOR A ROLLING MILL Filed Oct. 30, 1959 5 Sheets-Sheet 5 IA/VE/WOI. Pm. ELM/v by W W HGE United States Patent 5 Claims. (11. 80-56) It is a well-known fact that a strip to be rolled in a rolling mill provided with smooth rolls is in a position of non-stable equilibrium. In the absence of any means for stabilizing the material in an axial direction such as lateral guides or rearwardly drawing means for instance, any lateral shifting of the strip to one side or the other of the axis is speedily amplified and the strip soon reaches the trunnion of a roll.

In certain cases, it is not possible to resort to such stabilizing means for centering the strips axially of the rolling mill. In the case of a hot rolling mill rolling comparatively thin strips, said strips would be bruised upon engagement with lateral guides which could not furthermore retain the strip in a sufficient manner, by reason of the weakness of such a strip. In the case of rearwardly drawing means, they cannot be given a sufficient power for reliably guiding a strip raised to a high temperature, since the strip would stretch under the action of the stressing and form constricted areas, a phenomenon which would prevent rolling the material to a uniform size.

According to a known method, it is possible to guide a strip in a hot rolling mill by giving the rolls a concave outline. Practical rules have been established for the shape of the rolls in the successive stands of a continuous hot strip rolling mill; this guiding method which is generally applied in such continuous hot strip rolling mills shows the obvious drawback of producing a strip, the central part of which is thicker than the edges.

My invention has for its object a method for guiding strips of a considerable length in hot rolling mills, while avoiding the above-mentioned drawback. To this end, the present invention is based on an overcompensated rolling mill.

According to a further object of the invention, the mill is provided with a hydraulic closing system, as described in applicants United States Patent No. 3,075,417, granted on the copending application Serial No. 848,783 filed on October 26, 1959. The apparatus of the patent includes a small plunger piston measuring the operative pressure in a jack and acting in antagonism with a gauged spring and, according to the present invention, said spring is more yielding than would be the case if it were to accurately compensate the varying roll spring in the rolling mill, with a view to obtaining an overcompensation.

However, this stabilization of the position of the strip is obtained only when using a rolling mill which cannot ensure an unvarying thickness for the rolling material. Obviously, as a matter of fact, an overcompensated rolling mill will lead to a rolled material of a variable thickness, whenever the strip to be rolled shows a non-uniform thickness or hardness at the input of the rolling mill, said modification in thickness being reversed with reference to those which would be obtained with a non-compensated rolling mill.

A further object of the invention is to provide for stability of the location of the strip without resorting to a complete overcompensation of the adjustment of the rolling mill. To this end and in accordance with a further feature of my invention, the rolling mill is subjected Patented Nov. 17, 1%64 to means producing overcompensation, while simultaneously a correction is made to the adjustment on both sides of the rolling mill thus overcompensated, so as to cut out at any moment the eii'ects of the overcompensation-of the mill, as concerns its action on the thickness of the strip.

The invention covers also a mechanical arrangement for executing the method according to the invention, without any complete overcompensation, said arrangement being constituted by the above-mentioned hydraulic system ensuring overcompensation and wherein the meas uring plunger on each side of the rolling mill is coupled with an auxiliary plunger acting in the opposite direction and subjected to the pressure on the other side of the rolling mill, the corresponding operative cross-sectional areas a and B of the plungers on each side of the rolling mill being such that a-fi3 may assume a predetermined value corresponding to the accurate compensation of the spring, while the sum oc-i-B ensures stability of the strip positioning.

In order to provide a better understanding of the in vention, a preferred embodiment thereof will now be described, reference being made to the accompanying drawings, wherein:

FIG. 1 illustrates diagrammatically the shapes assumed by a strip after successive operations in a hot rolling mill having a concave roll outline.

FIG. 2 illustrates diagrammatically three positions of a strip in its transverse relationship with rolls having concave operative generating lines, in the same hot rolling mill.

FIG. 3 is a similar view showing three successive positions of a strip with reference to rolls having rectilinear operative generating lines in an overcompensated rolling mill according to the invention.

FIG. 4 illustrates diagrammatically an arrangement for the hydraulic closing of the rolls in a rolling mill, in association with compensating means for rolling mill spring.

FIG. 5 is a partial diagrammatic showing of the same arrangement incorporating further members, so as to execute the method according to the invention.

FIG. 6 is a diagrammatic View of an auxiliary arrangement cooperating with the arrangement according to FIG. 5.

FIG. 7 is a partial diagrammatic showing of another arrangement providing the same result as the arrangement according to FIGS. 5 and 6.

FIG. 8 is a similar view of last-mentioned arrangement, somewhat simplified.

FIG. 9 is a diagrammatic View of an arrangement according to FIG. 5 showing the parts on both sides of the rolling mill.

FIG. 10 is a similar view of an to FIGS. 7 and 8.

FIG. 11 is a diagrammatic view of an arrangement according to the invention adapted to operate in accordance with the skin-pass method.

FIG. 12 shows the arrangement of FIG. 4 mounted on a rolling mill of a type not provided with screws.

FIG. 1 illustrates, by way of example, the shape assumed during the successive rolling steps by a strip treated in a rolling mill, wherein the operative generating lines of the rolls engaging the material to be rolled have a slightly concave shape. All the outlines assumed by the strip are therefore thicker at the center than along the edges. The bulge thus obtained retains its relative value since each operative step ensures a same proportional reduction in thickness throughout the breadth of the strip. 7

FIG. 2 shows three successive transverse positions of the rolled material inside the rolls of the same rolling arrangement according mill as that referred to hereinabove. The position shown uppermost in FIG. 2 corresponds to a location of the material axially of the housing. The position illustrated in the middle of said FIG. 2 corresponds to a slight shifting of the material towards the left-hand side. By reason of said shifting and of the particular shape of the cylinder, the material is subjected to a reduction in thickness which is more considerable on the left-hand side than on the right-hand side.

Now, as well known by anyone skilled in the rolling procedure, an article rolled between non-corrugated rolls has always a tendency to escape through a shifting towards the side along which its thickness has been least reduced. In the present example, the material having, for any fortuitous reason, been shifted slightly towards the left will therefore return into its axial position as provided by the unequally distributed reduction to which it is subjected in this laterally shifted position. It is possible to repeat the same argument in the case of a slight shifting towards the right-hand side. It is thus apparent that the concave shape of the operative generating line of the cylinders produces a stabilization of the axial position of the strip whereby it is possible to obtain a correct guiding of the latter.

If the phenomena are analyzed which make the axial position of the strip be a position of non-stable equilibrium in a rolling mill, the rolls of which have a rectilinear outline, the conclusion is that its lack of stability is ascribable to the spring of the rolling mill i.e. to the fact that the distance separating the operative generating lines of the rolls increases with the pressure applied. As a matter of fact, if the strip passes slightly out of its axial position to be shifted, for instance, towards the lefthand side, the mill spring will cause the rolls to open slightly on the left-hand side, where the stress increases, while they move towards each other on the right-hand side where the stress decreases. Now, such a misadjustment of the rolls urges the strip towards the left-hand side and it will be readily understood that, since the effect reacts thus on its cause and increases its intensity, the strip will move at an accelerated speed towards the left-hand side. These considerations show that the spring is truly the reason for the instability of the position of the strip. This means that the guiding of the strip is more difficult when the rolling mill is less rigid and viceversa.

Now, certain well-known adjusting methods allow a correction of the adjustment of the rolling mill housing as a function of the stress required by the reduction in the thickness of the rolled material by reducing the rolling mill spring or by cutting out same. In this latter case, the rolling mill spring is considered as exactly compensated. If the correction of the adjustment of the rolling mill housing is larger than that actually required by the rolling mill spring the rolling mill is considered as overcompensated. The characteristic of such an adjusted condition is that the spacing of the rolls decreases when the stress acting on them increases.

PEG. 3 shows that in overcompensated rolling mills, the axial position of the strip is a stable position. The upper portion of said figure shows the material passing axially of the housing between rolls, the operative generating lines of which are rectilinear and parallel. In the next section of the figure, it is apparent that the material has been slightly shifted towards the left. By reason of said shifting, the stress on the left-hand upright is higher than the stress on the right-hand upright and, since the rolling mill is overcompensated, the rolls assume a nonparallel position, the left-hand side, which is subjected to a greater load, being tightened, while the right-hand side, which is subjected to a lesser load, is released. The material which has thus been subjected to a more considerable reduction on its left-hand edge than on its righthand edge will consequently return into its axial position, exactly as in the case disclosed hereinabove of a rolling between rolls, the operative generating lines of which are concave. If therefore for any fortuitous reason the material is shifted towards the left-hand side, the overcompensating means will urge it back into its proper axial position. The same would be the case if, for any fortuitous reason, the material were shifted towards the right-hand side. The misadjustment of the rolls produced by the overcompensation has therefore a tendency to cut out in all cases a possible misadjustrnent in position of the strip.

It is thus apparent that the use of overcompensated rolling mills for the automatic guiding of the strips allows operating with rolls, the operative generating lines of which are rectilinear under loaded conditions, so that it is possible to obtain strips having a uniform thickness throughout their breadth. This is an important advantage over the guiding methods resorted to hitherto.

it is obvious that this guiding method resorts to automatic roll tightening means for obtaining the required correction to the adjustment of the rolling mill. To this end, an advantageous embodiment consists in using as means for tightening or closing the rolls of the rolling mill that which is disclosed in applicants copending specification entitled Hydraulic arrangement for adjusting the spacing of the rolls of rolling mills and compensating spring, said copending application claiming priority of the French patent filed on October 31, 8 by Institut de Recherches de la Sidrurgie. It will be readily ascertained that the overcompensation obtained with such an arrangement is ensured by giving the spring acting in antagonism with the spacing-adjusting plunger piston, subjected to the operative pressure in the jack controlled by the spacing of the cylinders, a lesser stiffness than that required for providing an accurate compensation of the modifications in spring.

FIGS. 4 and 12 illustrate said arrangement. As appareat, the plunger piston 1 of a hydraulic jack, and its cylinder or casing 2 are inserted in the kinematic chain interconnecting the two rolls of a rolling mill. Said FIG. 12 shows that the housings H carry the system including in superposition the jack 2-1, the roll R in its chock C and the roll R in its chock C The plunger piston 1 assumes automatically a position for which the switch 3-4 is about alternatingly to close and open.

FIG. 4 shows the hydraulic circuit associated with the jack 1, 2. The cylinder 2 of the jack is connected to a control valve 6 by a pipe 5. The valve is operated by an electromagnet 11 against a return spring. In one valve position, hydraulic fluid drawn from a tank 9 is forced by a pump 8 through a pipe 7 and the valve 6 into the cylinder 2. In the other valve position, the fluid is released from the cylinder 2 to the tank 9 through a pipe 10.

Two contacts 3, 4 form a switch arranged in series with the valve magnet 11 and a current source. The contact 3 is suspended from the center of a spring 13 whose ends are fixedly supported. A plunger 14 mounted on the cylinder 2 abuts against the center of the spring 13 from above under the pressure of the fluid in the cylinder 2, and tends to move the contact 3 downward toward the contact 4. The latter is mounted on the jack piston 1 by means of a bracket 12 and of an adjusting screw 15. When the electromagnet 11 is energized, additional fluid is pumped into the cylinder 2 through the valve 6.

Under such conditions, the height h of the jack increases when the stress applied to the latter and, consequently, the fluid pressure increases. This allows compensating the roll spring or the elastic deformation of the housing. If the spring 13 on which the measuring and adjusting plunger 14 acts, has a stiffness which is less than that corresponding to the accurate compensation of the mill spring, this provides an overcornpensated rolling mill provided with the interesting property consisting in that it produces a stable position of equilibrium for the rolled strip axially of the cage. This property is obviously retained, whatever'may be the adjustment given simultaneously through the screws 15 to the contact-pieces on either side of the rollingmill. In particular, this property remains entire when the screws 15 on either side of the rolling mill are adjusted simultaneously and synchronously in accordance with the rolling stress, in a manner such that said adjustment of the screws 15 cuts out the excess compensation ascribable to the reduced stifiness of the springs 13. It is possible to obtain thus a rolling mill which is accurately compensated, while retaining, as far as the accurate guiding of the strip is concerned, the desired features of an overcornpensated rolling mill.

This arrangement may be of a dificult adjustment and, therefore, further arrangements according to the invention will now be described, which latter arrangements allow obtaining automatically the desired correction.

Thus, FIG. 5 illustrates the same overcompensated arrangement as FIG. 4, but with the difference that a small auxiliary plunger 16 is provided to measure a pressure in antagonism with an auxiliary spring 17. Said small auxiliary plunger is subjected to a pressure which is equal to the arithmetic average between the pressures in the jack on either side of the rolling mill. Such an average pressure may be obtained readily, as disclosed diagrammatically in FIG. 6, wherein two coaxial cylindrical elements 18, 19 of different diameter jointly constitute a piston which divides the cavity of a cylinder 18' into three chambers 18a, 18b, and Ida. The circular radial end face of the smaller element 18 is exposed in the chamber 18a to the pressure Pa in one of the jack cylinders 2 with which the chamber 18a communicates by means of a conduit 19a. The annular radial end face of the larger element 19 has the same area as the radial end face of the element 18 and is exposed in the chamber 18b to the pressure Pb prevailing in the other jack cylinder 2. The circular radial end face of the element Id has an area equal to the combined area of the end faces in the chambers 18a, 18b, and transmits to the hydraulic fluid in the chamber 180 a pressure which is (Pa+Pb)/2. The fluid acts upon the auxiliary plunger 16 through a conduit 17.

The arrangement illustrated in FIG. 5 is precisely duplicated on the other side of the rolling mill. The plunger 16 on the other side will be understood also to communicate with the chamber 18c in a manner not further illustrated. Both plungers act on springs having the same characteristics and are subjected to the same pressure. Each spring 17 is connected to the corresponding spring 13 by a linkage consisting of three pivotally connected bars 14a, 14b, 140. The bars 14a and 140 respectively depend from the spring 13, 17 and hold the intermediate bar 145) in an approximately horizontal position. The contact 3 is suspended from the center of the bar 14b.

The vertical movement of the contact 3 is thus the combined result of the pressure in the associated jack cylinder 2 as modified by the spring 13 to produce overcompensation of the mill, and of the average pressure in both jack cylinders. The plungers 14, 16 move in opposite directions under the action of applied pressure, and a high average pressure in both jack cylinders thus counteracts the effects of high pressure in the associated jack cylinder. Obviously, these plungers 16 may, if their cross-section and the stiffness of the spring acting in antagonism therewith are suitably selected, provide for the automatic correction obtained through rotation of the screws 15 in the first example given hereinabove.

The arrangement illustrated in FIG. 5 is actually of a difiicult execution in practice and it has been described only so as to help in the understanding of the description of a still further arrangement which is much simpler in its execution while its principle is the same as that of the arrangement which has just been described. Said further arrangement illustrated in FIG. 7 is identical with the general arrangement of FIG. 5, except for the fact that the plungers 16 exert, in the case of FIG. 7, a stress which is mechanically subtracted from that exerted by the plunger 14, as provided by the strap 20, said plungers 14 and 16 being subjected respectively to the pressure prevailing inside the adjacent jack and to the prevailing pressure inside the jack on the opposite side of the rolling mill.

A modified form of the apparatus of FIG. 7 is shown in FIG. 8. Each jack cylinder 2' contains two chambers 21' and 23' separated by a partition 22. The chamber 21 communicates with the pressure space in the associated jack and is connected to the valve 6 by pipe 5 in the manner evident from FIG. 4. The chamber 23 is connected to the pressure space of the remote jack by a pipe 19c.

Two plungers 21, 23 are normally urged outward of the chambers 21', 23' in opposite directions by the pressure of the fluids in the chambers. They are fixedly connected by a rod 22 which passes in sealing engagement through the partition 22'. The plunger 21 abuts against the center of a spring 13' with a force which is the difference of the forces acting on the annular end faces of the plungers 21, 23 adjacent the rod 22 in the chambers 21' and 2.3. The ends of the spring 13' are fixedly supported, and the spring carries a contact 3 as described with reference to FIG. 4.

The cross-sectional area of the plunger 21 is much greater than that of the plunger 23. The operative cross sectional area of each plunger is reduced by the cross section of the rod 22. It will be now shown that the arrangements according to FIGS. 7 and 8 provide the same results as the arrangement illustrated in FIG. 5, for which it has already been shown how the method according to the invention is practically executed thereby.

Turning now to the diagram of FIG. 9 corresponding to the arrangement of FIG. 5 and to the diagram of FIG. 10 corresponding to the arrangement of FIGS. 7 and 8, it is possible to write out the following equation for the first arrangement (FIG. 5):

x designating the displacement of the contact-piece 3 starting from its original location under the action of the pressures Pa and Pb prevailing in the jacks on either sides of the rolling mill, while R designates the stiffness of the springs-assumed to be identicaland a and b designate the cross-sectional areas of the two plungers.

For the second arrangement (FIGS. 7 and 8), the equation would be:

a B R Pa Pb assuming the stiffness of the springs is the same as in the preceding case, while a and ,8 designate the operative cross-sections of the plungers.

The two arrangements are therefore equivalent if:

The resultant force applied to the spring 13' on one side of the rolling mill in the arrangement of FTGS. 7 or 8 is aPa-,6Pb, and on the other side of the rolling mill otPb-liPd. If the strip being rolled is properly centered, the pressures Pa, Pb in the two jacks are equal:

Pa=Pb=P and the resultant force acting on the springs 13' on either side of the rolling mill is P(a-/i). If the strip is displaced toward one side in such a manner that Pa increased by AP and Pb decreases correspondingly by AP, the forces applied to the two springs 13 respectively assume the values on the other side. It is thus seen that exact compensation is assured by a force acting on the spring 13 and roportional to a-B when the strip is in the correct central position, and that the force exerted on the spring 13 increases in the case of deviation of the strip by a factor of AP(a+B) on one side and decreases by an equal factor on the other side. This factor which is a measure of the tendency of restoring the strip to its central position is characteristic of overcompensation and is a function of n+5.

The difference of the cross sectional areas oi-B is chosen so as to produce exact compensation of mill spring, whereby a strip having a constant means thickness is rolled. The difference ot{3 therefore must suit the char acteristics of the the rolling mill. The value of the sum 06+,B, however, may be selected at will, and an increase in this sum increases the stability of the strip position under otherwise equal conditions.

Furthermore, if a constant thickness of the rolled material, is not essential it is possible, while retaining the proper guiding of the strip as in the overcompensated mill, to obtain an anti-compensated rolling mill. This expression anti-compensated rolling mill is intended to describe a rolling mill wherein the mill spring is larger than the spring of the housing of a rolling mill which is not provided with adjusting means. Such a feature may be of interest in the case of rolling mills operating in accordance with the so-called skin-pass method which leads to a reduction in thickness as constant as possible, whatever may be the variations in thickness at the input of the rolling mill. A suitable arrangement is illustrated in FIG. 11. The device shown in FIG. 11 is closely similar to that shown in FIG. 8 and difi'ers therefrom by the following features. The plunger 21a which moves inward and outward of the chamber 21' in response to variations in the pressure Pa is directly attached to the switch contact 3. The plunger 23a whose piston face is in the chamber 23 moves outward under the pressure Pb prevailing in the remote jack against a spring 13" arranged to oppose upward movement of the fixedly connected plungers 21a, 23a. The effective piston cross-sectional area ,8 of the plunger 23a is larger than the eifective piston area a of the cooperating plunger 2101. In this case and during operation, the strip lying axially of the rolling mill and the pressures prevailing in the two jacks being equal, any increase in this pressure ascribable to an increase in thickness of the strip at the input of the rolling mill will correspond to an upward movement of the switch 3-4 and, consequently, a reduction in the total height h of the jack. A further adjusted condition is thus obtained for which 11 is less than that obtained with the preceding adjustment. It is thus apparent that the arrangement disclosed has for its result a slight release of the rolling mill when the thickness increases at the input of the latter. This is actually the result which is to be achieved in the case of a skin-pass rolling mill. Now, even if is larger than a, such as anti-compensated rolling mill retains the property shown by an overcompensated rolling mill as concerns stability of the strip along the axis of the rolling mill. Assuming, as a matter of fact, that the strip has a tendency to move nearer one side of the rolling mill incorporating adjusting means of the type illustrated in FIG. 8, the pressure will increase in the corresponding jack and decrease in the jack on the opposite side. These two modifications in pressure act in the same direction on the switch 3-4 and urge the contact-piece 3 downwardly. The height h of the jack will thereupon increase and, consequently, the rolling mill will tighten the rolls on the side illustrated in PEG. 8. A

similar arrangement will show that the rolling mill will be released on the opposite side. These modifications in adjustment are actually those which have for their result a return of the strip into an axial position with reference to the rolling mill. Thus, the property of an overcompensated rolling mill is retained as far as stability in position of the strip axially of the mill is concerned.

Obviously it is possible, without unduly widening the scope of the invention as defined by the accompanying claims, to imagine detail modifications and improvements and to resort to the use of equivalent means, without the embodiments described limiting by any means the scope of said invention.

in particular, the overcompensating means may be constituted by an arrangement different from that disclosed in applicants above mentioneo copending application and various means may be imagined for correcting the adjustment on either side of the overcornpensated rolling mili, with a view to avoiding the effects of this overcompensation on the actual operation of the mill.

What I claim is:

1. In a rolling mill having a predetermined mill spring, two rolls rotatable about respective axes for rolling a dcformable material between opposite faces of said rolls intermediate the respective end portions of said rolls, four bearing means respectively supporting said end portions, said bearing means constituting two pairs, the members of each pair supporting coordinated end portions of respective rolls and being movable toward and away from one another transversely of said axes, jack means coordinated to each of said pairs for normally urging the members of each pair of bearing means toward one another, each jack means having a cylinder element and a piston element axially slidable in said cylinder element, said elements being respectively connected to the members of the coordinated pair for movement therewith and defining a pressure space in said jack means, a source of pressure fluid, valve means movable for selectively admitting pressure fluid from said source to said space, and for releasing said fluid from the latter, and valve control means, the valve control means of each of said jack means including a first control member movable in response to the pressure in said space, and a second control member movable relative to said first control member, said second control member being operatively connected to said piston element for movement in response to the movement of said piston element in said cylinder element, a resilient member opposed to movement of said first control member, the stiffness of said resilient member being lower than a stifiness sufiicient to produce compensation of said spring of the rolling mill, whereby an overcompensation of the mill spring is obtained, and actuating means responsive to the relative position of said control members for actuating movement of said valve, whereby strips of a considerable length may be guided between the rolls and be urged into a stable axial position with reference to the rolls.

2. In a rolling mill as set forth in claim 1, means to take off at each side of the rolling mill the arithmetic mean of the increase of compensation beyond the value corresponding to an accurate compensation of the spring to keep the desired thickness of the rolled material.

3. In a rolling mill, in combination:

(a) a housing means;

(b) two pairs of bearings mounted in said housing for movement of the bearings of each pair relative to each other;

(e) two rolls, each roll having an axis and two axial end portions respectively received in a bearing of each pair of bearings for rotation about said axis, and for movement toward and away from the other roll when the bearings of said pairs move relative to each other;

(d) two jacks, each jack including a cylinder member and a piston member movable in said cylinder memti her, the members, of each jack being respectively connected to the bearings of an associated pair for moving the same relative to each other;

(e) valve means associated with each jack, and operative for alternatively supplying hydraulic fluid under pressure to the associated jacks and for releasing fluid from said associated jacks; and

(f) valve control means associated with each jack,

each control means including (1) a first movable control member;

(2) first plunger means operatively connected to the associated jack and responsive to pressure therein for moving said first control member in a predetermined direction;

(3) a first resilient member opposed to said first plunger means;

(4') second plunger means operativeiy connected to said two jacks for moving said first control member in opposition to said first pioneer means responsive to the arithmetic mean of the respective pressures in said two jacks;

(5) a second resiiient member opposed to said second plunger means;

(6) a second control member movable relative to said first control member responsive to the position of the piston member of the associated jack in the corresponding cylinder member; and

(7) valve actuating means for operating said valve means responsive to the relative position of said first and second control members.

4. In a rolling mill having a predetermined spring,

(a) housing means;

the

(12) two pairs of bearings mounted in said housing for movement of the bearings of each pair relative to each other;

(0) two rolls, each roll having an axis and two axial end portions respectively received in a bearing of each pair of bearings for rotation about said axis, and for movement toward and away from the other roll when the bearings of said pairs move relative to each other;

(d) two jacks, each jack including a cylinder member and a piston member movable in said cylinder member, the members of each jack being respectively connected to the bearings of an associat d pair for moving the same relative to each other;

(e) valve means associated with each jack, and opit erative for alternatively supplying hydraulic fluid under pressure to the associated jacks and for releasing fiuid from said associated jacks; and

(f) valve control means associated with each jack,

each control means including (1) two chambers connected to one of the members of the associated jack for movement With said one member relative to the other member, and respectively communicating with the cylinder members of two jacks for receiving fluid under pressure therefrom,

(2) two fixedly connected plunger means of difierent operative cross sectional area arranged in respective chambers for movement in opposite directions under the pressure of the fluid in the respective chambers,

(3) yieldably resilient means engaging said connected plunger means for opposing movement thereof under the pressure of the fluid in both chambers,

(4-) a first control member connected to said plunger means for joint movement therewith, (5) a second control member movable relative to said first control member, said second control member being operatively connected to the other member of said associated jack for movement therewith, and

(6) actuating means responsive to the relative position or said first and second control members for operating said valve means, whereby strips of considerable length may be rolled bebetween said rolls in a stable axial position.

5. in a mill as set forth in claim 4, the plunger means of larger cross-sectional area being arranged in the chamber communicating with the cylinder member of the associated jack, and the plunger means of smaller crosssectional area being arranged in the chamber communicating with the cylinder member of the other jack.

References (litter! in the file of this patent UNITED STATES PATENTS 581,078 Menne Apr. 20, 1897 1,669,559 Biggert May 15, 19-28 2,049,755 Meyer May 12, 1936 FOREIGN PATENTS 775,631 Great Britain May 15, 1957 

1. IN A ROLLING MILL HAVING A PREDETERMINED MILL SPRING, TWO ROLLS ROTATABLE ABOUT RESPECTIVE AXES FOR ROLLING A DEFORMABLE MATERIAL BETWEEN OPPOSITE FACES OF SAID ROLLS INTERMEDIATE THE RESPECTIVE END PORTIONS OF SAID ROLLS, FOUR BEARING MEANS RESPECTIVELY SUPPORTING SAID END PORTIONS, SAID BEARING MEANS CONSTITUTING TWO PAIRS, THE MEMBERS OF EACH PAIR SUPPORTING COORDINATED END PORTIONS OF RESPECTIVE ROLLS AND BEING MOVABLE TOWARD AND AWAY FROM ONE ANOTHER TRANSVERSELY OF SAID AXES, JACK MEANS COORDINATED TO EACH OF SAID PAIRS FOR NORMALLY URGING THE MEMBERS OF EACH PAIR OF BEARING MEANS TOWARD ONE ANOTHER, EACH JACK MEANS HAVING A CYLINDER ELEMENT AND A PISTON ELEMENT AXIALLY SLIDABLE IN SAID CYLINDER ELEMENT, SAID ELEMENTS BEING RESPECTIVELY CONNECTED TO THE MEMBERS OF THE COORDINATED PAIR FOR MOVEMENT THEREWITH AND DEFINING A PRESSURE SPACE IN SAID JACK MEANS, A SOURCE OF PRESSURE FLUID, VALVE MEANS MOVABLE FOR SELECTIVELY ADMITTING PRESSURE FLUID FROM SAID SOURCE TO SAID SPACE, AND FOR RELEASING SAID FLUID FROM THE LATTER, AND VALVE CONTROL MEANS, THE VALVE CONTROL MEANS OF EACH OF SAID JACK MEANS INCLUDING A FIRST CONTROL MEMBER MOVABLE IN RESPONSE TO THE PRESSURE IN SAID SPACE, AND A SECOND CONTROL MEMBER MOVABLE RELATIVE TO SAID FIRST CONTROL MEMBER, SAID SECOND CONTROL MEMBER BEING OPERATIVELY CONNECTED TO SAID PISTON ELEMENT FOR MOVEMENT IN RESPONSE TO THE MOVEMENT OF SAID PISTON ELEMENT IN SAID CYLINDER ELEMENT, A RESILIENT MEMBER OPPOSED TO MOVEMENT OF SAID FIRST CONTROL MEMBER, THE STIFFNESS OF SAID RESILIENT MEMBER BEING LOWER THAN A STIFFNESS SUFFICIENT TO PRODUCE COMPENSATION OF SAID SPRING OF THE ROLLING MILL, WHEREBY AN OVERCOMPENSATION OF THE MILL SPRING IS OBTAINED, AND ACTUATING MEANS RESPONSIVE TO THE RELATIVE POSITION OF SAID CONTROL MEMBERS FOR ACTUATING MOVEMENT OF SAID VALVE, WHEREBY STRIPS OF A CONSIDERABLE LENGTH MAY BE GUIDED BETWEEN THE ROLLS AND BE URGED INTO A STABLE AXIAL POSITION WITH REFERENCE TO THE ROLLS. 